<html>
<head>
    <script>
        window.existingCustomProperty = 1; 
        window.__proto__.windowPrototypeCustomProperty = 1; 
        window.Object.prototype.objectPrototypeCustomProperty = 1;
        window.location.customProperty = 1;
        window.history.customProperty = 1;
    </script>
</head>
<body>
    <iframe name="testiframe" src="data:text/html,<p>test iframe</p>"></iframe>
    <img name="testimage" src="data:image/jpg,">
</body>
</html>
